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![Research paper thumbnail of Selective surface chemistry of allyl alcohol and allyl aldehyde on Si(1 0 0)2×1: Competition of [2 + 2] C C cycloaddition with O–H dissociation and with [2 + 2] C O cycloaddition in bifunctional molecules](https://attachments.academia-assets.com/47589018/thumbnails/1.jpg)
](Surface Science, 2009
Competition between the C@C functional group with the OH group in allyl alcohol and with the C@O ... more Competition between the C@C functional group with the OH group in allyl alcohol and with the C@O group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2Â1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] C@O cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] C@C cycloaddition products. Temperaturedependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2Â1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] C@C cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2Â1 surface in selective reactions of the Si dimers with the OÀH group in allyl alcohol and with the C@O group in allyl aldehyde over the C@C functional group common to both molecules.
![Research paper thumbnail of Selective surface chemistry of allyl alcohol and allyl aldehyde on Si(1 0 0)2×1: Competition of [2 + 2] CC cycloaddition with OH dissociation and with [2 + 2] CO cycloaddition in bifunctional molecules](https://attachments.academia-assets.com/47589053/thumbnails/1.jpg)
](Surface Science, 2009
Competition between the C dbnd C functional group with the OH group in allyl alcohol and with the... more Competition between the C dbnd C functional group with the OH group in allyl alcohol and with the C dbnd O group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] C dbnd O cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] C dbnd C cycloaddition products. Temperature-dependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2×1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] C dbnd C cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2×1 surface in selective reactions of the Si dimers with the O-H group in allyl alcohol and with the C dbnd O group in allyl aldehyde over the C dbnd C functional group common to both molecules.
Journal of Physical Chemistry C, 2010
The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigat... more The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as densityfunctional theory (DFT) calculations. Three C 1s features can be attributed to the carboxyl C of bidentate acrylate (at 286.8 eV) and unidentate acrylate (at 289.3 eV), both resulting from OsH dissociation upon adsorption, and to their corresponding ethenyl C atoms (at 285.0 eV). The formation of bidentate acrylate at a low exposure is followed by that of unidentate acrylate at a higher exposure, with approximately equal populations for both adstructures at the saturation exposure. DFT calculations confirm that the bidentate acrylate adstructure gives the most stable adsorption structure configuration. The combined temperature-dependent XPS and TPD studies provide strong evidence for the formation of CO, ethylene, acetylene, and propene, with 60% of the C moiety from the adsorption configurations converted to SiC with increasing annealing temperature to 1050 K. A companion study on propanoic acid on Si(100)2×1 shows similar formation of bidentate and unidentate propanoate adsorption configurations and thermal evolution to only CO and ethylene. In both acrylic acid and propanoic acid, the respective OsH dissociation products appear to be preferred over the other reaction products, such as [O, C] bidentate formation, CsOH dissociation, CdC cycloaddition, CdO cycloaddition, and ene formation. The unreacted backbone of the acrylate adsorption configuration provides a reactive site for further functionalization by other molecules.
E-journal of Surface Science and Nanotechnology, 2009
We report first results about the ability of low density amorphous ice nanolayers to behave as a ... more We report first results about the ability of low density amorphous ice nanolayers to behave as a "matrix" and trap monomeric neutral glycine molecules at 125 K, a temperature much greater than the commonly used liquid He temperature region. FTIR-RAS spectra of those monomeric neutral glycine molecules adsorbed on low dense amorphous ice were obtained for the first time and indicate that glycine adsorbs molecularly with the carboxylic group and the nitrogen atom hydrogen-bonded to the ice surface.
Infrared reflection-absorption spectroscopy is used to investigate H2O ice deposited onto non-cry... more Infrared reflection-absorption spectroscopy is used to investigate H2O ice deposited onto non-crystalline (dimers [1]) and polycrystalline (infinite chains [1]) acetic acid films. The condensed water film grown at ˜135 K on these different substrates can be characterized as amorphous dense ice. The H2O molecules are shown to interact mainly with the carbonyl and the carboxyl oxygens, forming hydrogen bonds. Upon water adsorption on the non-crystalline acetic acid film, saturation of the change induced in the intensity of the C=O and C-O peaks occurs at an average H2O exposure of ˜ 2.52 L. The amount of H-bonding involving C=O or C-O (of acetic acid) and OH (of water) on the polycrystalline film has been reduced considerably compared to the situation on the non-annealed one, but saturation of the carbonyl oxygen even for a water exposure of 9 L has not been observed while the carboxyl oxygen saturates at ˜2.76 L. Thermal evolution studies for the ice film on non-crystalline and polycrystalline acetic acid films show that water co-evaporates with acetic acid likely as a water-acetic acid complex in the temperature range of 140-155 K, which continues until the entire ice film has been exhausted at 160 K. [1]: Q. Gao and K. T. Leung, J. Phys. Chem. B 109, (2005) 13263. .
Journal of Physical Chemistry C, 2009
The room temperature (RT) adsorption and thermal evolution of cis-and trans-dichloroethylene (DCE... more The room temperature (RT) adsorption and thermal evolution of cis-and trans-dichloroethylene (DCE) and their structural isomer, iso-DCE, on Ni(1 0 0) have been studied by vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS). For RT adsorption, both cis-and trans-DCE exhibit very similar EELS features that are different from those found for iso-DCE. These differences indicate the formation of different fragments upon RT adsorption. In particular, the primary adspecies for cis-and trans-DCE are ethane-1,1,2,2-tetrayl (HCÀCH) and acetylide-like ( ) adspecies along with a small amount of chlorovinyl adspecies, while ethylylidyne ( ) is the more plausible adspecies for iso-DCE. The differences in the adstructures upon dissociative adsorption at RT underline the important isomeric effects. Furthermore, both AES and TDS results for all three DCE isomers show that most of the Cl atoms produced by dechlorination remain on the surface and its surface concentration remains unchanged upon annealing the samples above 500 K. Upon further annealing to 550 K, the EELS spectra of all three isomers exhibit a broad feature near 1600 cm À1 , which suggests the formation of carbon clusters on the surface. The presence of surface Cl atoms therefore appears to prevent the C-C bond cleavage during thermal evolution of the adspecies on Ni(1 0 0). #
Surface Science, 2010
The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been inv... more The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1 s feature at 398.9 eV, attributed to a N-Si bond, indicates N-H dissociative adsorption. On the other hand, the presence of C 1 s features at 284.6 eV and 286.2 eV, corresponding to C=C and C-N, respectively, and the absence of the Si-C feature expected at 283.2 eV shows that [2 + 2] C=C cycloaddition does not occur at room temperature. These XPS data are consistent with the unidentate staggered and eclipsed allylamine conformer adstructures arising from N-H dissociation and not [2 + 2] C=C cycloaddition. The apparent conversion of the N 1 s feature for Si-N(H)-C at 398.9 eV to that for Si-N(H) at 397.7 eV and the total depletion of C 1 s feature for C-N at 286.2 eV near 740 K indicates cleavage of the C-N bond, leaving behind a Si-N(H)• radical. Furthermore, the C=C C 1 s feature at 284.6 eV undergoes steep intensity reduction between 740 K and 825 K, above which a new C 1 s feature at 283.2 eV corresponding to SiC is found to emerge. These spectral changes suggest total dissociation of the ethenyl fragment and the formation of SiC. Moreover, while the total N 1 s intensity undergoes a minor reduction (24%) upon annealing up to 1090 K, a considerable reduction (43%) is found in the overall C 1 s intensity. This observation is consistent with our TDS data, which shows the desorption of C-containing molecules including propene and ethylene at 580 K and of acetylene at 700 K. The lack of N-containing desorbates suggests that the dissociated N species are likely bonded to multiple surface Si atoms or diffused into the bulk. Interestingly, both the staggered and eclipsed N-H dissociative adstructures are found to have a less negative adsorption energy than the [N, C, C] tridentate or the [2 + 2] C=C cycloaddition adstructures by our DFT calculations, which suggests that the observed formation of N-H dissociative adstructures is kinetically favored on the Si(100)2 × 1 surface.
Surface Science, 2009
Competition between the C@C functional group with the OH group in allyl alcohol and with the C@O ... more Competition between the C@C functional group with the OH group in allyl alcohol and with the C@O group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2Â1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] C@O cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] C@C cycloaddition products. Temperaturedependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2Â1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] C@C cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2Â1 surface in selective reactions of the Si dimers with the OÀH group in allyl alcohol and with the C@O group in allyl aldehyde over the C@C functional group common to both molecules.
Surface Science, 2009
Competition between the C dbnd C functional group with the OH group in allyl alcohol and with the... more Competition between the C dbnd C functional group with the OH group in allyl alcohol and with the C dbnd O group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] C dbnd O cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] C dbnd C cycloaddition products. Temperature-dependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2×1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] C dbnd C cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2×1 surface in selective reactions of the Si dimers with the O-H group in allyl alcohol and with the C dbnd O group in allyl aldehyde over the C dbnd C functional group common to both molecules.
Journal of Physical Chemistry C, 2010
The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigat... more The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as densityfunctional theory (DFT) calculations. Three C 1s features can be attributed to the carboxyl C of bidentate acrylate (at 286.8 eV) and unidentate acrylate (at 289.3 eV), both resulting from OsH dissociation upon adsorption, and to their corresponding ethenyl C atoms (at 285.0 eV). The formation of bidentate acrylate at a low exposure is followed by that of unidentate acrylate at a higher exposure, with approximately equal populations for both adstructures at the saturation exposure. DFT calculations confirm that the bidentate acrylate adstructure gives the most stable adsorption structure configuration. The combined temperature-dependent XPS and TPD studies provide strong evidence for the formation of CO, ethylene, acetylene, and propene, with 60% of the C moiety from the adsorption configurations converted to SiC with increasing annealing temperature to 1050 K. A companion study on propanoic acid on Si(100)2×1 shows similar formation of bidentate and unidentate propanoate adsorption configurations and thermal evolution to only CO and ethylene. In both acrylic acid and propanoic acid, the respective OsH dissociation products appear to be preferred over the other reaction products, such as [O, C] bidentate formation, CsOH dissociation, CdC cycloaddition, CdO cycloaddition, and ene formation. The unreacted backbone of the acrylate adsorption configuration provides a reactive site for further functionalization by other molecules.
E-journal of Surface Science and Nanotechnology, 2009
We report first results about the ability of low density amorphous ice nanolayers to behave as a ... more We report first results about the ability of low density amorphous ice nanolayers to behave as a "matrix" and trap monomeric neutral glycine molecules at 125 K, a temperature much greater than the commonly used liquid He temperature region. FTIR-RAS spectra of those monomeric neutral glycine molecules adsorbed on low dense amorphous ice were obtained for the first time and indicate that glycine adsorbs molecularly with the carboxylic group and the nitrogen atom hydrogen-bonded to the ice surface.
Infrared reflection-absorption spectroscopy is used to investigate H2O ice deposited onto non-cry... more Infrared reflection-absorption spectroscopy is used to investigate H2O ice deposited onto non-crystalline (dimers [1]) and polycrystalline (infinite chains [1]) acetic acid films. The condensed water film grown at ˜135 K on these different substrates can be characterized as amorphous dense ice. The H2O molecules are shown to interact mainly with the carbonyl and the carboxyl oxygens, forming hydrogen bonds. Upon water adsorption on the non-crystalline acetic acid film, saturation of the change induced in the intensity of the C=O and C-O peaks occurs at an average H2O exposure of ˜ 2.52 L. The amount of H-bonding involving C=O or C-O (of acetic acid) and OH (of water) on the polycrystalline film has been reduced considerably compared to the situation on the non-annealed one, but saturation of the carbonyl oxygen even for a water exposure of 9 L has not been observed while the carboxyl oxygen saturates at ˜2.76 L. Thermal evolution studies for the ice film on non-crystalline and polycrystalline acetic acid films show that water co-evaporates with acetic acid likely as a water-acetic acid complex in the temperature range of 140-155 K, which continues until the entire ice film has been exhausted at 160 K. [1]: Q. Gao and K. T. Leung, J. Phys. Chem. B 109, (2005) 13263. .
Journal of Physical Chemistry C, 2009
The room temperature (RT) adsorption and thermal evolution of cis-and trans-dichloroethylene (DCE... more The room temperature (RT) adsorption and thermal evolution of cis-and trans-dichloroethylene (DCE) and their structural isomer, iso-DCE, on Ni(1 0 0) have been studied by vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS). For RT adsorption, both cis-and trans-DCE exhibit very similar EELS features that are different from those found for iso-DCE. These differences indicate the formation of different fragments upon RT adsorption. In particular, the primary adspecies for cis-and trans-DCE are ethane-1,1,2,2-tetrayl (HCÀCH) and acetylide-like ( ) adspecies along with a small amount of chlorovinyl adspecies, while ethylylidyne ( ) is the more plausible adspecies for iso-DCE. The differences in the adstructures upon dissociative adsorption at RT underline the important isomeric effects. Furthermore, both AES and TDS results for all three DCE isomers show that most of the Cl atoms produced by dechlorination remain on the surface and its surface concentration remains unchanged upon annealing the samples above 500 K. Upon further annealing to 550 K, the EELS spectra of all three isomers exhibit a broad feature near 1600 cm À1 , which suggests the formation of carbon clusters on the surface. The presence of surface Cl atoms therefore appears to prevent the C-C bond cleavage during thermal evolution of the adspecies on Ni(1 0 0). #
Surface Science, 2010
The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been inv... more The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1 s feature at 398.9 eV, attributed to a N-Si bond, indicates N-H dissociative adsorption. On the other hand, the presence of C 1 s features at 284.6 eV and 286.2 eV, corresponding to C=C and C-N, respectively, and the absence of the Si-C feature expected at 283.2 eV shows that [2 + 2] C=C cycloaddition does not occur at room temperature. These XPS data are consistent with the unidentate staggered and eclipsed allylamine conformer adstructures arising from N-H dissociation and not [2 + 2] C=C cycloaddition. The apparent conversion of the N 1 s feature for Si-N(H)-C at 398.9 eV to that for Si-N(H) at 397.7 eV and the total depletion of C 1 s feature for C-N at 286.2 eV near 740 K indicates cleavage of the C-N bond, leaving behind a Si-N(H)• radical. Furthermore, the C=C C 1 s feature at 284.6 eV undergoes steep intensity reduction between 740 K and 825 K, above which a new C 1 s feature at 283.2 eV corresponding to SiC is found to emerge. These spectral changes suggest total dissociation of the ethenyl fragment and the formation of SiC. Moreover, while the total N 1 s intensity undergoes a minor reduction (24%) upon annealing up to 1090 K, a considerable reduction (43%) is found in the overall C 1 s intensity. This observation is consistent with our TDS data, which shows the desorption of C-containing molecules including propene and ethylene at 580 K and of acetylene at 700 K. The lack of N-containing desorbates suggests that the dissociated N species are likely bonded to multiple surface Si atoms or diffused into the bulk. Interestingly, both the staggered and eclipsed N-H dissociative adstructures are found to have a less negative adsorption energy than the [N, C, C] tridentate or the [2 + 2] C=C cycloaddition adstructures by our DFT calculations, which suggests that the observed formation of N-H dissociative adstructures is kinetically favored on the Si(100)2 × 1 surface.